The present invention relates to the control of the upsetting pressure during resistance welding of a tube or pipe as made from flat, endless skelp or strip being formed into such a tube or pipe.
The making of tubing from skelp or strip is a process of long standing. The strip or skelp is formed into a tubular hollow (split tube) and adjoining or abutting edges are, for example, electrically resistance welded. In the past, it was up to the welder to determine and monitor the requisite parameters for welding such as the pressure under which the edges are forced against each other in the welding spot the temperature of welding, the speed or progression, etc.; significant experience was required to produce a salable product with but a few or no rejects.
It is apparent that temperature and speed measurement and control as well as control over the pressure is essential with emphasis on reproducing similar parameters under comparable conditions. U.S. Pat. No. 3,573,416 is an example for a welding procedure in which the upsetting pressure is measured among several other operating parameters for the resistance welding.
Many experiments and investigations concerning welding parameters failed because there are too many interfering factors. For example, dirt in the various mechanical parts such as guides and bearings, forces and their distribution on the periphery of the tube, etc. Measuring specifically (to the exclusion of other parameters) the local pressure which urges the two edges being, about to be or just having been welded together, is almost impossible, simply because any measuring results include inherently one or more interfering parameters which cannot be isolated.